While secondary metabolites of the fungus include useful compounds, they also include many compounds that present toxicity, called mycotoxin. At present, mycotoxin contamination of crops has become a serious problem all over the world. In order to obtain a safe food and ensure a stable supply thereof, there is a need for ways to control mycotoxin contamination.
Among mycotoxin contamination of crops, the most serious one is aflatoxin contamination of crops. It is known that aflatoxin is the strongest carcinogenic substance of the known natural substances. Since aflatoxin is a compound that is not degraded by a normal food preparation method, etc., the value of the compound allowed to be contaminated in crops is regulated to as low as 10 ppb. Thus, the loss due to the disposal of crops contaminated with aflatoxin reaches a large amount.
Aflatoxin is mainly produced by strains of Aspergillus flavus, and A. parasiticus, and is known to infect crops such as maize and peanut and produce aflatoxin under the tropical and subtropical environments (See, Non-Patent Literatures 1 and 2). Due to the climate change by the global warming in recent years, it is concerned that contamination may extend to the region with a climate other than tropical and subtropical climates.
In order to control aflatoxin contamination, basic research such as genomic analysis of aflatoxin-producing microorganism and identification of a gene that is involved in the production, and practical research such as acquisition of variety with resistance to infection and reduction of contamination by the competition with aflatoxin non-producing microorganism have been conducted. However, an efficient and drastic method for controlling aflatoxin contamination has not yet been established.
Possible methods for controlling aflatoxin contamination include, for example, a method in which an antifungal agent that inhibits the growth of aflatoxin-producing microorganism. However, strong antifungal agents have a problem in terms of safety. In addition, there is a possibility that the spread of strain resistant to the antifungal agents is caused.
Since aflatoxin is a secondary metabolite, it is considered that inhibition of the production thereof does not affect the growth of aflatoxin-producing microorganism. Thus, if a medical agent that inhibits only the production of aflatoxin specifically is available, such medical agent could provide an effective method for controlling contamination.
As a result of search for the substances that inhibit the production of aflatoxin, it was found that dichlorvos, an organophosphorus insecticide, and tricyclazole which inhibits melanin biosynthetic enzyme, have aflatoxin production inhibitory activity (See, Non-Patent Literature 3). However, these compounds have not come into practical use because the aflatoxin production inhibitory activity of these compounds is weak and there is a concern over the safety of the compounds themselves. In addition, there is a problem in selectivity of the inhibitory activity.
As mentioned above, there is a need for compounds that do not cause the spread of resistant strain and have an action to inhibit only aflatoxin production specifically. As a result of search, some compounds are found (Patent Literatures 1 and 2); however, in the present situation, an acceptable aflatoxin production inhibitor that is highly safe and is of practical use has not been found yet.    Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 09-241167    Patent Literature 2: JP-A No. 11-79911    Non-Patent Literature 1: Council for Agricultural Science and Technology., “Mycotoxins: Risks in Plant, Animal, and Human Systems”, CAST, Ames, Iowa, USA, 2003    Non-Patent Literature 2: Shun-ichi Udagawa, Setsuko Tabata, and Mitsuo Nakazato, “Mycotoxin”, Chuohoki, 2002    Non-Patent Literature 3: L. L. Zaika and R. L. Buchanan, J. Food. Prot., 50, 691 (1987)